As known, a bicycle bottom bracket comprises a shaft at the opposite ends of which a left pedal crank and a right pedal crank are respectively associable or associated. The bottom bracket is mounted on the bicycle housing the shaft in a housing box suitably provided in the bicycle frame. The rotation of the bottom bracket with respect to the housing box is obtained by inserting a pair of rolling bearings onto the shaft. The shaft is held in position in the housing box by caps that are screwed into the ends of the box or that are pressure-inserted into the ends of the box. In particular, in order to allow the shaft to rotate with respect to the box and to the caps, the rolling bearings are arranged between the caps and the shaft. Furthermore, in order to avoid movements of the shaft in a direction parallel to its rotation axis, each rolling bearing is held in position by shoulders provided, on the side facing towards the pedal cranks, on the shaft and, on the opposite side, by shoulders provided on the caps.
The rolling bearings therefore at least partially face the respective pedal cranks and are therefore partially exposed to external agents such as dust, water and mud that, during normal use of the bicycle, hit the area of the pedal cranks and of the housing box of the bottom bracket.
In order to avoid such external agents being able to reach the rolling bearings and compromise correct operation, solutions have been proposed wherein between each cap and the shaft there is a protective labyrinth of the rolling bearing. Such a labyrinth is made from rings fixedly connected to the shaft alternating with rings fixedly connected to the cap, so as to allow the rotation of the shaft with respect to the cap but avoid direct exposure of the rolling bearing to the external environment. Moreover, in order to protect the balls of the bearing from infiltration of water that passes through the aforementioned labyrinth, it has been proposed to insert an annular gasket fixedly connected to the slewing bearing of the bearing constrained to the cap and sliding on the slewing bearing constrained to the shaft.
The Applicant has noted that the provisions proposed are not a full solution, in other words they do not allow the rolling bearings to be effectively protected from external agents, in particular water.
The Applicant has indeed observed that, for example in the case of the bicycle being washed with pressurized water, the water easily passes through the aforementioned labyrinth and reaches the aforementioned annular gasket.
The Applicant has also noted that the water that reaches the gasket cannot pass back through the labyrinth in the opposite direction and tends to stay right in front of the bearing at the portion of gasket that slides on the slewing bearing constrained to the shaft, with inevitable leaking of water between gasket and slewing bearing.
The Applicant has also noted that the presence of clearance recovery systems of the bottom bracket, which usually are arranged between a rolling bearing and the respective pedal crank, creates substantial difficulties in making and applying the aforementioned labyrinth that is active precisely at the area in which the clearance recovery system is also present.
The Applicant has also noted that the mounting and maintenance of the protection system of the rolling bearing summarily described above are very complicated also due to the presence of a large number of components to be installed in the correct position.